1. Field of the Invention
The present invention relates to a radio apparatus having transmission directivity and a method of controlling the same, and more particularly, it relates to a radio apparatus employed in an adaptive array radio base station and a method of controlling the same.
2. Description of the Related Art
An adaptive array radio base station employing an array antenna has been recently put into practice as a radio base station for a mobile communication system such as a portable telephone. The operation principles of such adaptive array radio base stations are described in the following literature, for example:
B. Widrow, et al. xe2x80x9cAdaptive Antenna Systems,xe2x80x9d Proc. EEE, vol. 55, No. 12, pp. 2143-2159 (December 1967).
S. P. Applebaum, xe2x80x9cAdaptive Arrays,xe2x80x9d EEE Trans. Antennas and Propag., vol. AP-24, No. 5, pp. 585-598 (September 1976).
O. L. Frost, III, xe2x80x9cAdaptive Least Squares Optimization Subject to Linear Equality Constraints,xe2x80x9d SEL-70-055, Technical Report No. 6796-2, Information System Lab., Stanford Univ. (August 1970).
B. Widrow and S. D. Stearns, xe2x80x9cAdaptive Signal Processing,xe2x80x9d Prentice-Hall, Englewood Cliffs (1985).
R. A. Monzingo and T. W. Miller, xe2x80x9cIntroduction to Adaptive Arrays,xe2x80x9d John Wiley and Sons, New York (1980).
J. E. Hudson, xe2x80x9cAdaptive Array Principles,xe2x80x9d Peter Peregrinus Ltd., London (1981).
R. T. Compton, Jr., xe2x80x9cAdaptive Antennas-Concepts and Performance,xe2x80x9d Prentice-Hall, Englewood Cliffs (1988).
E. Nicolau and D. Zaharia, xe2x80x9cAdaptive Arrays,xe2x80x9d Elsevier, Amsterdam (1989).
FIG. 10 is a model diagram schematically showing the operation principle of such adaptive array radio base stations. Referring to FIG. 10, an adaptive array radio base station 1 includes an array antenna 2 formed by n antennas #1, #2, #3, . . . , #n. A first area 3 with slant lines shows the range capable of receiving radio waves from the radio base station 1. A second area 7 with slant lines shows the range capable of receiving radio waves from another radio base station 6 adjacent to the radio base station 1.
In the area 3, a portable telephone 4 serving as a terminal of a user A transmits/receives a radio signal to/from the adaptive array radio base station 1 (arrow 5). In the area 5, on the other hand, a portable telephone 8 serving as a terminal of another user B transmits/receives a radio signal to/from the radio base station 6 (arrow 9).
If the radio signal employed in the portable telephone 4 of the user A is by chance equal in frequency to that employed in the portable telephone 8 of the user B, the radio signal from the portable telephone 8 of the user B may act as an undesired interference signal in the area 3 depending on the position of the user B, to be mixed into the radio signal between the portable telephone 4 of the user A and the adaptive array radio base station 1.
In this case, the adaptive array radio base station 1 receives the radio signals from the users A and B in a mixed state if taking no measures, to disadvantageously disturb communication with the user A.
In order to eliminate the signal from the user B from the received signals, the adaptive array radio base station 1 employs the following structure and processing:
FIG. 11 is a block diagram showing the structure of an adaptive array 100. Referring to FIG. 11, the adaptive array 100 is provided with n input ports 20-1 to 20-n, in order to extract a signal of a desired user from input signals including a plurality of user signals.
Signals received in the input ports 20-1 to 20-n are supplied to a weight vector control part 11 and multipliers 12-1 to 12-n through switching circuits 1xe2x80x941 to 10-n.
The weight vector control part 11 calculates weight vectors w1i to w1n with a training signal corresponding to the signal of a specific user previously stored in a memory 14 and an output of an adder 13. Each subscript i indicates that the weight vector is employed for transmission/receiving to/from an i-th user.
The multipliers 12-1 to 12-n multiply the input signals from the input ports 20-1 to 20-n by the weight vectors w1i to w1n respectively and supply the results to the adder 13. The adder 13 adds up the output signals from the multipliers 12-1 to 12-n and outputs the result as a received signal SRX(t), which in turn is also supplied to the weight vector control part 11.
The adaptive array 100 further includes multipliers 15-1 to 15-n receiving an output signal STX(t) from the adaptive array radio base station 1, multiplying the same by the weight vectors w1i to w1n supplied from the weight vector control part 11 and outputting the results. The outputs of the multipliers 15-1 to 15-n are supplied to the switching circuits 10-1 to 10-n respectively. The switching circuits 10-1 to 10-n supply the signals received from the input ports 20-1 to 20-n to a signal receiving part 1R in receiving, while supplying signals from a signal transmission part 1T to the input/output ports 20-1 to 20-n in signal transmission.
The operation principle of the signal receiving part 1R shown in FIG. 11 is now briefly described.
In order to simplify the illustration, it is hereafter assumed that the number of antenna elements is four and the number of users PS from which signals are simultaneously received is two. In this case, signals RX1(t) to RX4(t) supplied from the antennas to the receiving part 1R are expressed as follows:
RX1(t)=h11Srx1(t)+h12Srx2(t)+n1(t)xe2x80x83xe2x80x83(1)
RX2(t)=h21Srx1(t)+h22Srx2(t)+n2(t)xe2x80x83xe2x80x83(2)
RX3(t)=h31Srx1(t)+h32Srx2(t)+n3(t)xe2x80x83xe2x80x83(3)
RX4(t)=h41Srx1(t)+h42Srx2(t)+n4(t)xe2x80x83xe2x80x83(4)
where RXj(t) represents a signal received in a j-th (j=1, 2, 3, 4) antenna, and Srxi(t) represents a signal transmitted from an i-th (i=1, 2) user.
Further, hji represents a complex factor of the signal from the i-th user received by the j-th antenna, and nj(t) represents noise included in the j-th received signal.
The above equations (1) to (4) are expressed in vector forms as follows:
X(t)=H1Srx1(t)+H2Srx2(t)+N(t)xe2x80x83xe2x80x83(5)
X(t)=[RX1(t), RX2(t), . . . RXn(t)]Txe2x80x83xe2x80x83(6)
H1=[h1i, h2i, . . . , hni]T, (i=1, 2)xe2x80x83xe2x80x83(7)
N(t)=[n1(t), n2(t), . . . , nn(t)]Txe2x80x83xe2x80x83(8)
In the above equations (6) to (8), [ . . . ]T shows transposition of [ . . . ].
In the equations (5) to (8), X(t) represents an input signal vector, Hi represents a received signal factor vector of the i-th user, and N(t) represents a noise vector respectively.
As shown in FIG. 11, the adaptive array 100 outputs a signal composited by multiplying the input signals from the respective antennas by the weighting factors w1i to w1n as the received signal SRX(t). The number n of the antennas is four.
When extracting the signal Srx1(t) transmitted from the first user, for example, the adaptive array 100 operates under the aforementioned preparation as follows:
An output signal y1(t) from the adaptive array 100 can be expressed by multiplying the input signal vector X(t) by a weight vector W1 as follows:
y1(t)=X(t)W1Txe2x80x83xe2x80x83(9)
W1=[w11, w21, w31, w41]Txe2x80x83xe2x80x83(10)
The weight vector W1 has the weighting factor wj1 (j=1, 2, 3, 4) multiplied by the j-th input signal RXj(t) as its element.
Substitution of the input signal vector X(t) expressed in the equation (5) into y1(t) expressed in the equation (9) gives the following equation:
y1(t)=H1W1TSrx1(t)+H2W1TSrx2(t)+N(t)W1Txe2x80x83xe2x80x83(11)
When the adaptive array 100 ideally operates, the weight vector control part 11 sequentially controls the weight vector W1 by the well-known method described in the above literature, to satisfy the following simultaneous equations:
H1W1T=1xe2x80x83xe2x80x83(12)
H2W1T=0xe2x80x83xe2x80x83(13)
When the weight vector W1 is completely controlled to satisfy the equations (12) and (13), the output signal y1(t) from the adaptive array 100 is ultimately expressed as follows:
y1(t)=Srx1(t)+N1(t)xe2x80x83xe2x80x83(14)
N1(t)=n1(t)w11+n2(t)w21+n3(t)w31+n4(t)w41xe2x80x83xe2x80x83(15)
In other words, the signal Srx1(t) transmitted from the first one of the two users is obtained as the output signal y1(t).
Referring to FIG. 11, the input signal STX(t) for the adaptive array 100 is supplied to the transmission part 1T in the adaptive array 100 and supplied to first inputs of the multipliers 15-1, 15-2, 15-3, . . . , 15-n. The weight vectors w1i, w2i, w3i, . . . , wni calculated by the weight vector control part 11 on the basis of the received signals in the aforementioned manner are copied and applied to second inputs of the multipliers 15-1, 15-2, 15-3, . . . , 15-n respectively.
The input signal STX(t) weighted by the multipliers 15-1, 15-2, 15-3, . . . , 15-n is transmitted to the corresponding antennas #1, #2, #3, . . . , #n through the corresponding switching circuits 10-1, 10-2, 10-3, . . . , 10-n respectively, and transmitted into the area 3 shown in FIG. 10.
The users A and B are identified as follows: The radio signal from each portable telephone is transmitted in a frame structure. The radio signal from the portable telephone is roughly formed by a preamble formed by a signal series known to the radio base station and data (voice etc.) formed by a signal series known to the radio base station.
The signal series of the preamble includes a signal string of information for determining whether or not the user is a desired user for making communication with the radio base station. The weight vector control part 11 of the adaptive array radio base station 1 contrasts the training signal corresponding to the user A fetched from the memory 14 with the received signal series and performs weight vector control (decision of the weighting factor) to extract a signal seeming to include the signal series corresponding to the user A.
FIG. 12 is a diagram imaging transfer of the radio signal between the user A and the adaptive array radio base station 1.
The signal transmitted through the same array antenna 2 as that in receiving is subjected to weighting targeting the user A similarly to the received signal, and hence the transmitted radio signal is received by the portable telephone 4 of the user A as if having directivity to the user A.
When outputting the radio signal to the area 3 showing the range capable of receiving radio waves from the adaptive array radio base station 1 as shown in FIG. 10 while properly controlling the adaptive array antenna 2 as shown in FIG. 12, it follows that the adaptive array radio base station 1 outputs a radio signal having directivity targeting the portable telephone 4 of the user A as shown in an area 3a in FIG. 12.
As described above, the adaptive array radio base station 1 can transmit/receive a radio signal having directivity targeting a specific user, whereby a path division multiple access (PDMA) mobile communication system can be implemented as described below:
In order to efficiently utilize frequencies in a mobile communication system such as a portable telephone, there are proposed various transmission channel allocation systems including the aforementioned PDMA system.
FIG. 13 shows arrangements of channels in various communication systems including frequency division multiple access (FDMA), time division multiple access (TDMA) and PDMA systems.
With reference to FIG. 13, the FDMA, TDMA and PDMA systems are now briefly described.
In the FDMA channel allocation system shown in FIG. 13, analog signals from users 1 to 4 are frequency-divided and transmitted through radio waves of different frequencies f1 to f4. The signals from the users 1 to 4 are separated through a frequency filter.
In the TDMA system shown in FIG. 13, a digitized signal from each user is time-divided every constant time (time slot) and transmitted through radio waves of different frequencies f1 to f4. The signal from each user is separated through a frequency filter and time synchronization from a base station and a mobile terminal unit of each user.
On the other hand, the PDMA system shown in FIG. 13 spatially divides a single time slot at the same frequency for transmitting data of a plurality of users. In the PDMA system, the signal of each user is separated through a frequency filter, time synchronization between a base station and a mobile terminal unit of each user and a mutual interference eliminator employing an adaptive array or the like.
When employing the PDMA system, not only radio signals transferred between different radio base stations and two users corresponding to the radio base stations must be separated so as to not mutually interfere with each other but also mutual interference between radio signals transmitted/received to/in different users with the same frequency and the same time slot in the area belonging to the same adaptive array radio base station 1 must be eliminated.
In the example shown in FIG. 12, it is possible to prevent the radio signal from the terminal of the user B transmitting/receiving the radio signal to/from the adjacent base station 6 from interfering the radio signal of the user A transmitting/receiving the radio signal to/from the adaptive array radio base station 1 by utilizing directivity through the adaptive array antenna 2.
If the distance between the users A and B is reduced, i.e., if the users A and B are within the area belonging to the same radio base station 1, it may be difficult to sufficiently eliminate interference between the radio signals of the users A and B only with the directivity through the adaptive array antenna 2.
Further, it is advantageous to widen an area covetable by a single radio base station, for example, in consideration of the cost for constructing the base station. In consideration of the aforementioned interference between radio signals of users, however, such widening of the area covered by a single base station results in increase of the strength of radio waves from the single base station, leading to the possibility of increasing mutual interference between the radio waves and those from an adjacent base station. In other words, the area coverable by a single base station cannot be much widened, in order to prevent mutual interference.
An object of the present invention is to provide a radio apparatus having transmission directivity capable of suppressing mutual interference of radio signals between users and a method of controlling the transmission directivity in a system transmitting/receiving radio signals.
Another object of the present invention is to provide a radio apparatus having transmission directivity capable of spreading a cover area of a radio base station and a method of controlling the transmission directivity in a system transmitting/receiving radio signals in the PDMA system.
Briefly stated, the present invention is directed to a radio apparatus comprising a receiver and a transmitter.
The receiver has receiving directivity for performing path division multiple access with a plurality of terminal units, and separates a received signal from a specific terminal unit from a received radio signal.
The receiver includes a plurality of received signal separators extracting the received signal by multiplying the received radio signal by a received weight vector corresponding to each terminal unit and a received strength measurer for measuring received radio strength of each terminal unit.
The transmitter has transmission directivity for performing path division multiple access, and generates a transmit signal having directivity to a specific terminal unit.
The transmitter includes a plurality of transmit signal generators generating the transmit signal having directivity by multiplying a transmit signal by a transmit weight vector obtained by weighting the received weight vector in response to the received radio strength from the received radio strength measurer.
According to another aspect of the present invention, a method of controlling a radio apparatus having transmission directivity for performing path division multiple access with a plurality of terminal units comprises steps of deriving a received weight vector corresponding to each terminal unit in real time and separating a received signal from the terminal unit, measuring received radio strength of each terminal unit on the basis of a received radio signal and the separated received signal, deriving a transmit weight vector obtained by weighting the received weight vector in response to the received radio strength from the received radio strength measurer for each terminal unit, and generating a transmit signal having directivity by multiplying a transmit signal by the transmit weight vector.
Accordingly, a principal advantage of the present invention resides in that, according to the inventive radio apparatus capable of controlling transmission directivity and the inventive method of controlling transmission directivity, transmission power from the base station is suppressed when transmitting/receiving a radio signal to/from a terminal close to the base station so that interference with another cell or another user can be reduced.
Another advantage of the present invention resides in that transmission power from the base station is increased when transmitting/receiving a radio signal to/from a terminal far from the base station, whereby the maximum reachable distance of the radio signal transmitted from the base station is increased in an established manner.